The present invention relates to a harmonics survey system for surveying harmonics superimposed to a power transmission (distribution) line particularly capable of surveying the harmonics in an optional power transmission line in a non-contact manner.
In a known art, there is provided a system, as such harmonic survey system, for surveying harmonics in accordance with a detected result of a current sensor such as shown in FIG. 4 as a schematic block diagram of a known harmonics survey system.
In the harmonics survey system of FIG. 4, a current transformer CT for an instrument is disposed to a distribution line 100 of a receive-side transformer 300, and harmonics superimposed to the distribution line 100 is detected by a harmonics detection circuit 120 in accordance with a value detected by the current transformer CT. The harmonics detection circuit 120 is adapted to operate and then detect current values of respective degrees or orders of the harmonics, and concrete current values corresponding to the harmonics of the respective degrees are displayed by a display section.
The harmonics detection circuit 120 can detect the harmonic through a fast Fourier transform process. In such case, in a primary stage of the fast Fourier transform process, the current detected by the current transformer CT is sampled with a predetermined sampling frequency to thereby convert the current to a digital signal.
Further, another system for preventing a harmonic fault is also disclosed in Japanese Patent Laid-open (KOKAI) Publication No. SHO 61-199420, which will be shown in FIG. 5.
With reference to FIG. 5, the condenser system as a conventional harmonics survey system is provided with condensers C1, C2 and C3 and linear reactors L1, L2 and L3 connected in series to the condensers C1, C2 and C3, respectively, and also provided with induction coils L10, L20 and L30 magnetically coupled with the linear reactors L1, L2 and L3, respectively. These induction coils L10, L20 and L30 have output ends to which outputs from harmonics detection circuits 121, 122 and 123 composed of synchronizing circuits synchronized with the coils to be detected are applied as harmonics detection signals. The condensers C1, C2 and C3 are also connected with branch lines 110R, 110S and 110T branched from distribution lines 100R, 100S and 100T of a power supply system, respectively, thus constituting the series circuits together with the condensers C1, C2 and C3 and the linear reactors L1, L2 and L3. A breaker 10 is interposed between the branch lines 110R, 110S and 110T and the distribution lines 100R, 100S and 100T so as to establish an electrical connection therebetween and separate them from each other.
The harmonics detection circuits 121, 122 and 123 connected to the output ends of the induction coils L10, L20 and L30 magnetically coupled with main coils of the linear reactors L1, L2 and L3 are composed of tuning (synchronizing) circuits having tuning characteristics having detection objects of harmonic orders such as fifth harmonics or seventh harmonics, and outputs generated upon the detection of such harmonics are utilized as harmonics detection signals. An alarm 130 operated in response to the harmonics detection signal serves to separate the breaker 110 in response to an alarming operation. A buzzer, lamp or other display means may be utilized in substitution for the alarm 130 or in combination therewith. Further, the harmonics detection circuits 121, 122 and 123 may be accommodated in a container or disposed outside thereof.
In general, electric current flowing the main circuits of the linear reactors L1, L2 and L3 of the characters mentioned above has a linearly proportional relationship to intensity of a leakage magnetic field, and accordingly, voltages proportional to the harmonic current flowing the main coils are outputted to the induction coils L10, L20 and L30 magnetically coupled with the main circuits of the linear reactors L1, L2 and L3 through the leakage magnetic field.
When the harmonic current of the detection objective order flows to the linear reactors L1, L2 and L3, the induction coils L10, L20 and L30 generate voltages in proportion to the harmonic current, and these voltages are detected by the harmonics detection circuits 121, 122 and 123 to thereby generate the harmonics detection signals. In response to these signals, since the alarm 130 is operated, it is known that the harmonic current flows into the condensers C1, C2 and C3 as condenser system. In response to the operation of the alarm 130, the breaker 110 is separated or this fact may be displayed on a display means.
The harmonics detection circuits 121, 122 and 123 may have small energization power even if it serves to energize only the alarm 130, and accordingly, the induction coils L10, L20 and L30 having small capacities may be also utilized, so that no influence is applied to magnetic fluxes caused by the linear reactors L1, L2 and L3.
As mentioned above, according to the conventional harmonics survey system, there can be surveyed only the fact whether the harmonics at portions of the distribution lines 100, 100R, 100S and 100T, to which the current transformer CT for an instrument or induction coils L10, L20 and L30 are connected, are superimposed or not, and it is impossible to survey the existence (presence) of the harmonics at the other portions of these distribution lines to which current transformer CT or induction coils are not connected, providing a problem.
Furthermore, in the conventional harmonics survey system, since the current values are obtained and displayed every time of the respective orders of the harmonics, it is required to consider influences to respective equipments or elements every time of the respective orders, also providing a problem of difficulty in the total judgement. Concretely, even in a case where the current values of the harmonics of the respective orders are within ranges of preset allowable values, when the harmonics of the respective orders totally act, significant influence will be given to, for example, a high pressure phase advance condenser or linear reactor, resulting in an occurrence of harmonic fault.
Further, in any conventional harmonics survey system mentioned above, in order to survey the harmonics at optional portions other than the specified or predetermined portions of the distribution lines 100, 100R, 100S and 100T, it is necessary to survey the harmonics through direct or indirect contact to the distribution lines, thus being dangerous for workers particularly in a case of high voltage current.